Google disclosed Android M for the developer preview, new additions included are changes to permissions.
Permissions for Apps can trigger requests at runtime, users are given options to allow the permission to be changed. Benefits to users allow your apps to get running faster, giving much easier access in managing all app permissions in the settings. With M, developers, can design apps prompting for permission to get granted.
The more devices that upgrade to M, the more the development of apps the more critical the permissions behavior flow to test